Butadiene-1,3 is an important petrochemical organic raw material, a monomer of synthetic rubber and an uppermost component in C4 distillate as well. In raw materials of petrochemical olefin, it ranks only next to ethylene and propylene. It can pose the reaction of substitution, addition, cyclization, and polymerization due to conjugated double bond contained in its molecule, which enable it to be widely applied to the area of synthetic rubber and organic composition. It can be fabricated to various rubber products such as (cis-butadiene rubber) BR, styrene butadiene rubber (SBR), nitrile butadiene rubber, styrene-butadiene-styrene (SBS), acrylonitrile-butadiene-styrene (ABS) resin. In addition, it can not only produce organic petrochemical products like adiponitrile, hexamethylene diamine, nylon 66, 1,4-butyl glycol, but also adhesives, gasoline additives, etc. The utilization is highly broad.
The source of butadiene-1,3 in industry is mainly from two means. One is to be obtained by dehydrogenation and extraction of C4 distillate from refinery. Currently, only a few countries, which possess abundant resource of butane and butylene, are making use of it. The throughput accounts for about 8%. The other one is to be attained by extraction of mixed C4 distillate co-produced from ethylene cracker. This method is in the ascendant in economy due to low cost and is the main source of butadiene-1,3 globally at present. The output accounts for around 92%.
The butadiene-1,3 separation process fed by mixed C4 distillate co-produced from ethylene cracker, butadiene-1,3 extraction process, as taking different solvent, is classified to three categories, acetonitrile (ACN) process, dimethyl formamide (DMF) process and N-methyl pyrrolidone (NMP) process.
The yield of butadiene-1,3 extraction of acetonitrile (ACN) process, dimethyl formamide (DMF) process and N-methyl pyrrolidone (NMP) process is about 97%. The rest 3% of butadiene-1,3, except butadiene dimer, is carried off by butane&butalene distillate, vinyl acetylene offgas, methyl acetylene offgas and waste C4C5 discharged from 2nd extractive fractionator bottom separately. In view of the feasibility of construction investment and routine operation cost of butadiene extraction unit, in the process of plant design and practical production, the content specification of butane&butalene distillate, vinyl acetylene offgas, methyl acetylene offgas and waste C4C5 discharged from 2nd extractive fractionator bottom are assured. The loss of butadiene-1,3 in vinyl acetylene offgas, methyl acetylene offgas is in relation to the content of vinyl acetylene and methyl acetylene in C4 feed. The higher content of vinyl acetylene and methyl acetylene is in C4 feed, the more butadiene-1,3 is losing. Because the loss of butadiene-1,3 caused by vinyl acetylene offgas accounts for large proportion in total, in order to avoid losing butadiene-1,3, measure taken in most of technology is to improve vinyl acetylene content in vinyl acetylene offgas to reduce butadiene-1,3 content. Meanwhile, for the purpose of safety, butane&butylene distillate is added for dilution. Though the measure works to some extent, there is no big change on it. The loss of butadiene-1,3 is still considerable.
Along with the development of auto industry, the demand for rubber products like tires is constantly increased. The demand for butadiene-1,3, as a main raw material of rubber production, is progressive accordingly. Therefore, many manufactories commit themselves to challenge butadiene extraction unit to get more and more production load, even produce with over-load at the cost of increasing loss of butadiene-1,3. Even so, many manufactories, whose development is in the restriction of production, invest to build new butadiene extraction units and the newly-built butadiene extraction unit tends to large scale. Some manufactories own two or three butadiene extraction units.
In consideration of increasing demand of butadiene-1,3, one approach is to build new butadiene extraction unit. However, it will take large cost and long period. There are around 20 sets of butadiene extraction units in China and about 100 sets across the world. Therefore, updating and tapping the potential of the existing butadiene unit, improving the yield and capacity of it is another option to expand output of butadiene-1,3. It is an effective route with low investment and fast effect as well.